Heavy duty industrial battery chargers are employed in many different types of operations--such as heavy industry, food processing and storage, etc.--all of which may use "industrial trucks" such as battery-powered pallet tractors, fork lift trucks, etc. The batteries in such industrial trucks may have amp-hour ratings of from 200 amp-hours to 1,800 amp-hours, and they may have anywhere from six to 36 cells. Such storage batteries are of the lead-acid type, and usually have a terminal voltage per cell, when fully charged, of from 2.4 to 2.6 volts. During use, an industrial storage battery or bank of storage batteries in an industrial truck may have its charge reduced virtually to zero; but such fully discharged battery may be required for use the following day, so that it may be fully recharged in the shortest possible time and without overheating. Thus, the need exists for battery chargers having suitable charging characteristics, and sufficient charging rates and voltages. Normally, however, an industrial battery charger is specifically designed only for batteries having one particular amp-hour rating; and such industrial battery chargers are adapted to recharge or back-charge a storage battery of the designated size and rating in a given period of time--usually 8 to 12 hours.
Several modes of operation of industrial battery chargers have been particularly followed in the past. Very often, industrial battery charges have provided a constant current, whereby a charging current is delivered to a storage battery at a substantially constant rate. Most often, such constant current battery chargers have operated at two charging rates, a high initial charging rate and a low final charging rate.
The other general mode of operation of industrial battery charges has been taper charging, which is characterized by an initially very high charging current output which tapers because of the nature of the current output control within the charger until a specific voltage per cell of the battery is reached, whereupon a low-current output characteristic of the charger is initiated. In the past, the monitoring and transfer circuitry of a tapered characteristic battery charger which initiates the transfer from high to low current output was essentially the same as in a constant current charger, i.e. the transfer from high to low output current is a step function of the charger. The output current during low-current operation of a taper charger according to the prior art is generally controlled by a ballast resistor or linear reactor; and taper chargers as well as constant current chargers are also usually equipped with a total shut-off at a given time, so as to avoid overcharging the storage battery.
More recently, the present inventor has provided a battery charging apparatus which has recognized that during the early stages of recharging a storage battery, constant current high level charging provides the best performance--with the best protection for the battery--and at the same time precludes high DC shocks to the battery and excessively high power consumption. Accordingly, the present inventor has provided a prior art battery charger which has an initial constant, high current output, which then transfers to a taper (constant voltage) output, and finally a trickle charge. Such a charger is described in detail in my U.S. Pat. No. 3,848,173, issued Nov. 12, 1974.
One drawback of most prior art battery chargers has been the fact that, although suitable temperature compensating circuitry, line regulation circuitry, etc., can be inserted in a charger, the circuits and relays which control the step transfer from high to low output--or which control the termination of taper charging--must be essentially fail-safe in order to assure that the transfer to low current output occurs. Unfortunately, such equipment can be easily triggered by a vibration or shock, so that the step transfer may be initiated much too early; and if that occurs, a full charge of the storage battery is not achieved. Otherwise, the fail-safe characteristics and features may be overridden thereby leading to a potentially dangerous over charging operation of the battery.
As noted, storage batteries, and particularly industrial storage batteries, may have considerably different sizes and amp-hour ratings, which require different charging rates; but the principal remains that a constant potential charging mode which transfers the operation of the storage battery charging apparatus from a high level to a low level or to a trickle charging mode, provides the greatest protection for storage batteries having the designated ratings for which any one storage battery charging apparatus may be adapted. This invention, therefor, provides means by which storage batteries having the same voltage ratings but somewhat different amp-hour ratings than the name plate rating of the charger--up to 200%--may also be charged by any one specific charger, within limits, by altering certain of the control characteristics and parameters of the charger.
The present invention also recognizes that the owners and operators of battery powered industrial equipment whose batteries are being charged by battery chargers according to the present invention may wish to know, as early as possible, if there is an incipient failure of their industrial batteries, before any substantial damage may occur or a potentially dangerous situation concerning the installation and operation of the battery may occur.
Accordingly, the present invention provides a battery charging apparatus which also functions as a surveillance system whereby the state of a battery of known name plate characteristics (i.e., terminal voltage and amp-hour rating) may be determined particularly if it is beyond normal limits; and at the same time, a battery charging apparatus is provided whereby a visual--and, if necessary, audible--signal is given and which may not be cancelled or overridden by the apparatus, thereby reasonably assuring that an operator check of the battery will follow.
Improved battery charged circuitry is provided by the present invention, particularly having regard to energy efficient solid state devices and transformers, etc.
Further, improvements are provided whereby the operating condition of the battery charger, in association with a battery of known rating, may be under constant surveillance irrespective of the ambient temperature, age of the battery, state of sulphation of the battery, etc. so long as the overall characteristics of the battery are within predetermined but fairly broadly set limits.